HW2: MIPS ISA Profs. Daniel A. Menasce, Yutao Zhong, and Duane King Fall 2017 Department of Computer Science George Mason University

Transcription

1 HW2: MIPS ISA Profs. Daniel A. Menasce, Yutao Zhong, and Duane King Fall 2017 Department of Computer Science George Mason University Task: Due October 13 th, 23:59pm No Late Submissions Accepted There are 2 parts to this assignment: part 1: written exercises for Ch2; part 2: MIPS programming. Basic rules regarding assignment implementation and submission: Total points of this assignment: 100. Team Allowed. Maximum 2 per Team. State clearly names and G# s in all files. If you have a group of two, only one needs to submit the required zip file as described below. But names and G# s of group members must be on ALL submitted files. The other member must just submit a one-page pdf stating team member names and IDs. Members of a group must attend the same section of CS465. What to submit: follow these steps to prepare and submit a ZIP file a. Prepare a PDF file for Part 1 with answers to questions named as "cs465_hw2_lastname1_lastname2.pdf" (for 2-member teams), or "cs465_hw2_lastname1.pdf" (for 1-member teams); b. For Part 2, name your MIPS source code as "cs465_hw2_lastname1_lastname2.asm"(for 2-member teams), or "cs465_hw2_lastname1.asm" (for 1-member teams). Do NOT submit it as a.pdf. As in all programming assignments, your code must be very well commented. A description of your algorithm must be included as part of your header comment. c. Place both files in a folder and rename the folder to be "cs465_hw2_lastname1_lastname2"(for 2-member teams), or "cs465_hw2_lastname1" (for 1-member teams). Then compress it to a ZIP file (instead of compressing and then renaming). How to submit: Submission will be made via a blackboard link available to you. Plagiarism is not permitted in any form. I enforce the university policy and honor code. Use Piazza and office hours for questions if you need help. Part 1. Written Exercise for MIPS (40%) Notes: A large portion of (or all) points will be taken off if you only answer with a number. You must show steps to justify your answer. Answers must be legible, especially if you scan to generate your.pdf. Page 1 of 5

2 1. (10 pts) Pseudo-instructions can be implemented using MIPS real instructions. For example: Pseudo instruction Definition Implementation mov rdest, rsrc Copy value from register rsrc to register rdest add rdest, rsrc, $0 Provide a sequence of MIPS instructions that implement each of the pseudo-instructions below. You are NOT allowed to use any pseudo-instruction in your answer. You must comment your code well to explain the idea/algorithm. a. neg rdest, rsrc # put the negative of register rsrc into register rdest # only integers; no need to consider overflow b. sge rdest, rsrc1, rsrc2 # set register rdest to 1 if register rsrc1 is greater # than or equal to rsrc2 (assume both are signed # integers), and to 0 otherwise 2. (10 pts) Consider the following MIPS code: add $s0, $0, $0 add $t0, $0, $0 L1: slt $t1, $t0, $s2 beq $t1, $0, L4 sll $t1, $t0, 2 add $t1, $t1, $s1 lw $t2, 0($t1) slt $t1, $t2, $0 bne $t1, $0, L2 sub $s0, $s0, $t2 addi $t0, $t0, 2 j L1 L2: add $s0, $s0, $t2 L3: addi $t0, $t0, 2 j L1 L4: 1) Write an equivalent C code for the given MIPS code, assuming registers-variable mappings as: $s0-t, $s2-n, $s1-base address of an integer array A. 2) Assume that register $s2 is initialized to be 20, how many MIPS instructions will be executed for the given sequence? Assume there is no branch delay slot. 3. (10 pts) Translate function foo into MIPS assembly language. You must follow MIPS register usage conventions discussed in the textbook. Assume the function declaration of bar is int bar(int x, int y);. The code for function foo is as follows: int foo (int a, int b, int c){ return bar(a,b) + bar(a,c) } Page 2 of 5

3 4. (10 pts) Assuming we are executing an instruction at address 0x : 1) If the instruction word is 0x8D , what will be the address of the next 2) If the instruction word is 0x , what will be the address of the next 3) If the instruction word is 0x A, what will be the address of the next Show calculation steps to justify your answer. Assume there is no branch delay slot. Part 2. MIPS Programming (60%) MIPS Decoder. For this assignment, you will write a program that should accept machine code (as hex numbers) from the user, decode and print the corresponding MIPS assembly. Main program: Your main program must perform the following tasks: o Accept a string from the user that is always 8 characters long excluding the ending newline. o Extract the numeric value from the input string and print it as a binary. o Call subroutine extract() (details below) and print the format type (I/J/R) of the instruction. If the instruction is not in the list to be considered below, print "not supported". o Call subroutine extract() and print the destination register number of the instruction. If there is no destination register, print "none". If the specified destination register is wrong or instruction not supported, print "invalid". o Assumptions:! You can assume only lower case letters ('a' to 'f') will be used for hex values.! You can assume only a subset of MIPS instructions need to be considered: add, addi, sub, slt, lw, sw, beq, j. Required subroutines: You must define a subroutine int extract(int instruction, int left, int right). Parameters: o Parameter instruction is a MIPS instruction word, which is a 32-bit unsigned number. o Parameters left and right mark which bits from instruction should be extracted. You can assume they are unsigned integers. This subroutine needs to extract bits between left and right (inclusive) from the 32- bit binary instruction and return it as an unsigned integer. The 32 digits in instruction are numbered from 31 (most significant) to 0 (least significant). If the specified bit range is invalid (out-of-bound, left>right, etc), return -1. Examples given the instruction as the binary pattern below: digit: Page 3 of 5

4 o extract(0x ,31,26) " 0 o extract(0x ,15,11) " 8 o extract(0x , 5, 0) " 32 o extract(0x ,17,17) " 1 //left==end o extract(0x ,35,28) " -1 //out-of-bound o extract(0x , 2, 8) " -1 //left<right Requirements: o You must declare your subroutine to be global. Use these two lines to start your subroutine definition:.globl extract extract: o Your definition must follow MIPS register usage conventions as discussed in our textbook and slides. o You must mark clear the start and end of your subroutine. o A description of the algorithm of this subroutine must be included in your header comments. Hints: You may need to call the subroutine extract() multiple times in your main program to decode the instruction. You may need to use la to load an address into a register. ASCII encoding of symbols can be useful. You can turn on/off ASCII in MARS to inspect the memory content for the input string. You may find system calls useful to read in string or print a value in certain format. A quick reference for the subset of MIPS instructions your decoder must support: MIPS opcode funct MIPS opcode funct add 0x00 0x20 addi 0x08 X sub 0x00 0x22 slt 0x00 0x2a lw 0x23 X sw 0x2b X beq 0x04 X J 0x02 X Sample runs (user input in underlined blue, with newline displayed explicitly): Instruction to decode? Binary pattern to decode: Format type: R-type Destination register: 8 Instruction to decode? ae Binary pattern to decode: Page 4 of 5

5 Format type: I-type Destination register: none Instruction to decode? Binary pattern to decode: Format type: not supported Destination register: invalid Grading rubric: Code submission 5/60 Comments and algorithm 5/60 Assembled with no error 5/60 Required subroutine 20/60 Main program 25/60 Page 5 of 5